Poisonous and Allergy Plants

Cultural History of Poisonous Plants


  • Identifying poisonous plants accompanies finding edible plants in ancient foraging societies
    • utilized to capture prey
    • ‘toxic’ from Greek ‘toxikon’ = arrow poison


  • Ebers Papyrus list plant toxins known to Egyptians
    • agents of war
    • capital punishment


  • Renaissance age in Europe was full of renowned ’poisoner’s who rose to power


  • Thousands of plants known to contain poisons
    • many in our backyards!

Poisonous Plants in the Wild: Curare

  • Curare is arrow poison used by S. American tribes
    • causes quick paralysis


  • Over 70 species, from different tribes,used to make curare


  • Blocks nerve impulses at the junction of nerve and muscle
    • turbocurarine eventually isolated
    • used in surgery because effects reversible

Curare: How to make a poison dart

Backyard Poisonous Plants

  • Many common landscape plants are poisonous or fatal!
    • often to children


  • Oleander has more then 50 toxic compounds
    • planted in CA & southern states
    • hot dogs roasted on sticks can be fatal


  • Yews (Taxus spp.) can lead to respiratory or cardiac failure
    • grown as hedges


  • Rhododendron/Azaleas have poisonous leaves
    • tea made from leaves, flowers, pollen can be deadly
    • Delaware Indians used tea as suicide potion
    • blocks nervous regulation of heart

Backyard Poisonous Plants: Ricin

  • Spruge family (Euphorbiaceae) contains poison milky sap
    • Poinsettia, crown of thorns, pencil tree cactus


  • Castor bean (Ricin communis) has deadly toxic seeds
    • ingestion of 1 seed can kill a child


  • Toxic protein ricin inhibits protein synthesis in the intestinal wall
    • causes clumping of red blood cells
    • symptoms are nasty
    • symptoms do not develope for hours or days!
    • most deadly natural poison known


  • Poison cigarette in Breaking Bad

Poisonous Plants to Livestock


  • Numerous plants poisonous to sheep and cattle
    • can be passed to humans (milk)


  • White snakeroot impacted settlements west of Appalachian mtns
    • all plant parts contain toxic alcohol tremetol
    • cattle ingestion lead to ‘trembles’
    • human who drink milk had similar symptoms
    • blocks breakdown of lactic acid in liver


  • Milk vetches (locoweeds) toxic to horse, sheep, goats & cattle
    • widespread in western US
    • contain alkaloids that impact CNS
    • lead to paralysis

Plants that Cause Mechanical Injury


  • Plants can puncture with spines, thorns, prickles, burrs or hairs


  • In cacti, spins are modified leaves!
    • wards off animal predation
    • can be barbed or not barbed


  • Some plants have ‘stinging hairs’ that also inject chemical irritants
    • Stinging nettle family
    • hollow hairs like syringe
    • strangely also edible

Insecticides from Plants

  • Review: plants produce many secondary compounds
    • many reduce palatability for insects


  • Pest chemical defenses: bitter, toxic or alter life cycle
    • these ‘poisons’ can be harnessed by humans


  • Pyrethrum = made from Chrysanthemum flower
    • nerve poison for household insects
    • common in flea medications
    • may bioaccumulate in streams


  • Rotenone = roots from tropical legumes
    • nervous system paralysis in fish
    • used by indigenous peoples to catch fish
    • common garden insecticide

Allergy Plants


  • Certain plants or plant parts are capable of causing allergic conditions to sensitive individuals


  • Reactions considered hypersensitive reactions
    • immune systems differentiates ‘non-self’
    • produce immune response


  • Multiple pathways for allergies
    • respiratory from pollen
    • skins reactions to oils/resins
    • food allergies

Respiratory Allergies: Hay Fever Plants


  • ~20% of humans suffer significant allergies
    • hay fever and asthma most common


  • Hay fever: respiratory reactions to pollen
    • mild symptoms but long lasting
    • 17 million visits to physician each year


  • Plants causing hay fever are wind-pollinated
    • abundant amounts of small pollen


  • Glycoproteins, allergenic pollen proteins
    • proteins trigger growth of pollen tube
    • trigger immune response in humans

Respiratory Allergies: Ragweed



  • Ragweed, Ambrosia spp, most notorious hay fever plant
    • annual or perennial herbs
    • name means “food of the gods”


  • 1,000’s of small flowers release 1 billion pollen grains
    • release August - September
    • may be longer in southern states
    • 1 million tons of pollen each year


  • Invasive and spreading in Europe
    • introduced on grain shipments after WW1

Climate Change and Hay Fever Plants


  • Increasing temperatures alter growing seasons for plants
    • spring-flowering plants most sensitive


  • May trigger earlier starts to pollen season
    • may also increase pollen amounts


  • Elevated CO2 experiments show increase growth of ragweed
    • higher pollen production
    • study found increase in allergenic proteins
    • later frost dates increase ragweed season

Contact Dermatitis

  • Allergic reaction of skin to something touched
    • delayed hypersensitivity


  • Poison ivy, Toxicodendron readicans, cashew family
    • widespread in US & Canada
    • leaves alternate w/ 3 leaflets
    • leaf margins show several forms
    • 1 of every 2 people allergic


  • Poison oak & sumac less widespread


  • Urushiol, a resin, is allergen
    • slight bruising of leafs releases resin
    • binds to skin proteins rapidly

Food Allergies

  • ~4% of US population suffers from food allergies
    • greatest in children under 3
    • 100’s of foods cause reactions


  • Symptoms are wide-ranging
    • diagnosis difficult


  • Peanut most important allergen as most commonly involved in anaphylaxis
    • food packages indicate common allergens


  • Can GMO’s have hidden allergens?
    • soybean w/ gene from Brazil nut
    • StarLink corn

Latex Allergies

  • Latex is a milky exudate produced by many plants
    • hydrocarbons, alkaloids, resins, terpenes


  • Natural source of rubber, Hevea brasiliensis
    • hydrocarbons w/ elastic properites


  • Natural rubber latex found in gloves, tubing & medical supplies
    • 70% of rubber synthetic but natural superior


  • ~4% of population allergic to latex
    • symptoms from hives to inflammation
    • companies focus on low-allergen latex